The invention relates in general to a recording apparatus such as, in a preferred example, a printhead and, more specifically, to a printhead assembly that facilitates cleaning of the printhead. More particularly, the invention relates to a printhead assembly having a printhead with a plurality of shift register stages supporting a plurality of actuators, the shift registers stages being located on one side of the recording elements of the printhead, such as inkjet nozzles, to facilitate cleaning of the printhead""s nozzles.
Without limiting the scope of the invention, its background is described in connection with thermal inkjet printers, as an example. Modern printing relies heavily on inkjet printing techniques. The term xe2x80x9cinkjetxe2x80x9d as utilized herein is intended to include all drop-on-demand or continuous inkjet printer systems including, but not limited to, thermal inkjet, piezoelectric, and continuous, all of which are well known in the printing industry. Essentially, an inkjet printer produces images on a receiver medium, such as paper, by ejecting ink droplets onto the receiver medium in an image-wise fashion. The advantages of non-impact, low-noise, low-energy use, and low cost operation, in addition to the capability of the printer to print on plain paper, are largely responsible for the wide acceptance of inkjet printers in the marketplace.
The printhead is the device that is most commonly used to direct the ink droplets onto the receiver medium. A printhead typically includes an ink reservoir and channels which carry the ink from the reservoir to one or more nozzles. Typically, sophisticated printhead systems utilize multiple nozzles for applications such as high-speed continuous inkjet printer systems, as an example. Continuous inkjet printhead device types include electrostatically controlled printheads and thermally steered printheads. Both printhead types are named according to the means used to steer ink droplets ejected from nozzle openings.
It is well known in the art of inkjet printing that multiple actuators or heating elements per inkjet nozzle can be used. For example, U.S. Pat. No. 4,751,531 describes the use of a two heater printing nozzle while U.S. Pat. No. 4,695,853 describes the use of a vertical array of 9 heating elements per nozzle. In order to optimize drop formation conditions, it is preferred to utilize independent control circuits for such multi-actuator print nozzle configurations.
Inks for high speed ink jet printers, whether of the continuous or drop-on-demand type, must have a number of special characteristics. For example, the ink should incorporate a nondrying characteristic, so that drying of ink in the ink ejection chamber is hindered or slowed to such a state that by occasional spitting of ink droplets, the cavities and corresponding nozzles are kept open. The addition of glycol facilitates free flow of ink through the inkjet chamber. Of course, the inkjet printhead is exposed to the environment where the inkjet printing occurs. Thus, the previously mentioned nozzles are exposed to many kinds of air born particulates. Particulate debris may accumulate on surfaces formed around the nozzles and may accumulate in the nozzles and chambers themselves. That is, the ink may combine with such particulate debris to form an interference burr that blocks the nozzle or that alters surface wetting to inhibit proper formation of the ink droplet. The particulate debris should be cleaned from the surface and nozzle to restore proper droplet formation. In the prior art, the cleaning mechanism may consist of a brush, wiper, sprayer, vacuum suction device, and/or spitting of ink through the nozzle.
At the same time, there are practical space limitations with respect to the number of layers necessary to implement the control circuits as well as limitations in the number of interconnections that are practical in order to make the design useful and operable. These type of design constraints require the use of serial shift registers to bring the print data to the printhead during printing. Between the stated design constraints lies an optimum solution for maintaining of clean multi-actuated printheads.
Thus, inkjet printers can be said to have the following problems: the inks tend to dry-out in and around the nozzles resulting in clogging of the nozzles; cleaning nozzles that have limited accessibility due to the placement of the control electronics poses extra demands on the design of printhead assembly as well as the cleaning members used.
Accordingly, what is needed is a way of organizing the printhead assembly such that minimal interference with cleaning is facilitated. A printhead assembly that arranges the shift register stages and actuators to facilitate cleaning of the nozzles would provide numerous advantages.
The present invention provides a solution to dealing with the task of cleaning a multi-actuated configuration printhead that has limited space due to the control electronics. The invention provides a printhead assembly with the control circuitry advantageously placed to facilitate cleaning of the printhead assembly.
Therefore, according to one embodiment, disclosed is an inkjet printhead comprising a plurality of nozzles arranged in an array for ejecting ink to form an image on a receiver member and a plurality of actuators associated with each respective nozzle, each actuator being separately drivable to affect ejection of ink from the respective nozzle. The printhead further comprises a plurality of shift registers stages, each stage being associated with a respective nozzle actuator and nozzle actuators associated with each nozzle being associated with different shift register stages. A cleaning assembly is provided for cleaning the nozzles. The shift register stages being adapted to shift data from one stage to a next stage to distribute data to the different stages, wherein the shift register stages are arranged to facilitate cleaning of the plurality of nozzles. According to one specific embodiment, the shift register stages are positioned on the same side of the printhead thereby providing sufficient space for the cleaning mechanism and the nozzles to be moved relative to each other.
Further disclosed is an inkjet printhead assembly comprising a plurality of nozzles having corresponding nozzle openings for delivering ink onto a specified receiver medium and a plurality of shift registers operably coupled to a plurality of actuators associated with said nozzles and adapted to cause ink to be delivered through said nozzles openings in the direction of said receiver medium. The printhead assembly further comprises print data drivers operably coupled to the plurality of shift registers via a plurality of interconnections, wherein said shift registers are arranged all to one side of the nozzles to facilitate cleaning of the plurality of nozzles. In one specific embodiment, the plurality of actuators comprise heaters. In another specific embodiment, the shift registers and their respective electrical interconnections using a wire-bonding technique are positioned on one side of said plurality of nozzles thereby providing sufficient space for the cleaning mechanism to be moved relative to the nozzles.
In accordance with another aspect of the invention, there is provided a method of providing image data in the printer apparatus, the method comprising providing a plurality of recording elements arranged in an array for recording of an image on a receiver medium; providing a plurality of actuators associated with each respective recording element each actuator being separately drivable to affect recording by a respective recording element; providing a cleaning assembly for cleaning the recording elements; providing a plurality of shift register stages, each stage being associated with a respective different actuator, each recording element being associated with plural different shift register stages and shifting data from one stage to a next stage to distribute data to the different stages, the shift register stages and their respective wire-bond interconnects being located all to one side of the array of recording elements; and advancing the cleaning assembly relative to the array of recording elements wherein the shift register stages and their respective wire-bond interconnections are sufficiently positioned away from the recording elements to facilitate cleaning of the recording elements by the cleaning assembly without the cleaning assembly damaging the shift register circuits.
A technical advantage of the present invention is a cost effective method of facilitating cleaning of a printhead assembly in a thermal inkjet printhead.
Another technical advantage includes optimum compromise between the length of shift registers and number of heaters to be controlled. In one printhead configuration, twenty 128-bit shift registers are able to operate a 1280 nozzle assembly.